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    <title>Document</title>
    <script>
      //1.新增数组元素 修改length长度
      var arr = ["1", "2", "3"];
      console.log(arr.length);
      arr.length = 5; //将数组长度修改为了5
      console.log(arr);
      console.log(arr.length);
      //2.新增数组元素 修改索引号 追加数组元素
      var arr1 = [1, 2, 3, 4, 5, 6];
      arr1[6] = 777;
      console.log(arr1);
    </script>
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